PowerPoint® Presentation by Jim Foley Sensation and Perception PowerPoint® Presentation by Jim Foley © 2013 Worth Publishers

Module 17: Basic Principles of Sensation and Perception

Your brain will interpret, perceive these topics as they enter your sense organs: Sensation vs. Perception, Bottom-Up vs. Top-Down Processing Transduction and Thresholds Sensory Adaptation Perceptual Set Context Effects on perception Emotion/Motivation effects No animation.

Sensation vs. Perception “The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment.” “The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events.” The brain receives input from the sensory organs. The brain makes sense out of the input from sensory organs. Click to reveal shortened definition; click again to reveal rest of animation.

Making sense of the world Top-down processing: using models, ideas, and expectations to interpret sensory information What am I seeing? Bottom-up processing: taking sensory information and then assembling and integrating it Click to reveal definitions for bottom-up and top-down processing. Is that something I’ve seen before?

Do you see a painting or a 3D bottle? What’s on the bottle? Kids see eight to ten dolphins. Why do you think kids see something different than adults? Click to reveal answer and to circle the dolphins. Answer to the question: Top-down processing by children uses different experiences and different models; they are likely to have seen more images of dolphins than images of a nude embrace. Adults also do more top-down processing, and are more likely to “see” objects that aren’t fully there. This shows that “seeing” involves the process of perception, not just the process of our eyes taking in information.

Top-down Processing You may start to see something in this picture if we give your brain some concepts to apply: “tree” “sidewalk” “dog” “Dalmatian” Click to reveal sidebar and hints one by one.

From Sensory Organs to the Brain The process of sensation can be seen as three steps: Reception-- the stimulation of sensory receptor cells by energy (sound, light, heat, etc) Transduction-- transforming this cell stimulation into neural impulses Transmission--delivering this neural information to the brain to be processed Automatic animation. Psychophysics refers to the study of the psychological effects of the forms of energy (heat, light, sound) that we can detect.

Anything below this threshold is considered “subliminal.” Thresholds The absolute threshold refers to the minimum level of stimulus intensity needed to detect a stimulus half the time. Anything below this threshold is considered “subliminal.” No animation. Instructor: You could first present this question using a specific sense, such as “How loud does a sound have to be before you can detect it?”

When Absolute Thresholds are not Absolute Signal detection theory refers to whether or not we detect a stimulus, especially amidst background noise. This depends not just on intensity of the stimulus but on psychological factors such as the person’s experience, expectations, motivations, and alertness. No animation. For example, parents of newborns can detect a faint baby’s cry that for others would not stand out from background noise.

below our threshold for being able to consciously detect a stimulus Subliminal Detection Subliminal: below our threshold for being able to consciously detect a stimulus Although we cannot learn complex knowledge from subliminal stimuli, we can be primed, and this will affect our subsequent choices. We may look longer at the side of the paper which had just showed a nude image for an instant. Click to reveal bullets and example. Research seems to show that: 1) we can sense something without being aware of it. 2) we can be briefly primed, but not enduringly influenced, by subliminal stimuli.

The “Just Noticeable Difference” Difference threshold refers to the minimum difference (in color, pitch, weight, temperature, etc) for a person to be able to detect the difference half the time. Weber’s law refers to the principle that for two stimuli to be perceived as different, they must differ by a constant minimum percentage and not a constant amount (e.g. 1/100th of the weight, not 2 ounces). No text animation, but the background color on the right side of the screen changes very slightly (and slowly) a couple of times. Ask students to raise their hand if they see a difference in color in the background of this slide. On a click, you can change the color again, and another click changes it back to the original color.

Sensory Adaptation To detect novelty in our surroundings, our senses tune out a constant stimulus. The rock in your shoe or the ticking of a clock are more difficult to sense after a while. We don’t notice this visually because normally our eyes are constantly moving. However, if you concentrate on keeping your eyes in one spot, you’ll see the effects, as your eyes adjust to stimuli in the following slides. Click to reveal bullets. To prepare for this slide, at the beginning of class you could ask students to tuck a pen behind one ear, and by the time they get to this slide, ask if they feel it. Or ask whether they feel the cell phone in their pockets, and then ask them to switch to the opposite pocket and see if they notice it more.

Automatic animation. Instructor: you can tell students, “This will push your motion sensors into sensory adaptation. For this to work, you must stare at the white dot in the center and never move your gaze. When the motion stops, quickly stare at a nearby doorway, window, or a face next to you. Decide now what you will look at.”

Perceptual Set Perceptual set is what we expect to see, which influences what we do see. Perceptual set is an example of top-down processing . Click to reveal second picture. Loch Ness monster or a tree branch? Flying saucers or clouds?

Perceptual set can be “primed.” Old woman Ambiguous Young woman Click to reveal second picture. Instructor: if you used this extra example, you can ask one half the class to focus on the image on the left, the other to look right. Then click and the ambiguous image appears, and the class can raise hands about which of the two images they see, to see if priming influenced their perception.

Context Effect on Perception In which picture does the center dot look larger? Perception of size depends on context. The text at the bottom of the screen will appear on click, and is mean to appear only AFTER you do the “spelling” test below. Instructor: The point of the test is to demonstrate how context, affected/primed by the previous word you stated, can affect which word they perceived. You can state to students, “Six word spelling test! You cannot ask questions; just take a guess and listen for the next word. Write these words down: Double. Pear. (Students may, if “double” gives them context, write “pair.”) Apple. Payor. (Students may, when primed by “apple”, write “pear.”) Payee. Pair. (Here, students might be confused, or some may write “payor.”) Spelling test answers: double pear apple payor payee pair Did context affect which word you wrote?

Effect of Emotion, Physical State, and Motivation on Perception Experiments show that: destinations seem farther when you’re tired. a target looks farther when your crossbow is heavier. a hill looks steeper with a heavy backpack, or after sad music, or when walking alone. something you desire looks closer. Click to reveal bullets. After reading the last bullet, click again to zoom the banana split.